Gas turbines (gas turbine plants), for cooling of the hot parts, especially the combustion chamber and the turbine through which flows the hot gas, use either cooling fluids, which are extracted from the compressor at a suitable pressure, are sometimes also additionally aftercooled, and, after cooling of the hot parts has been carried out, are added to the turbine flow, or closed cooling circuits which are supplied from an external cooling fluid source, in most cases with steam. In the latter cases, which are frequently to be found in combined cycle power plants, the cooling heat can often be additionally utilized in the downstream process. A further possibility, which is described in EP 0899425, for example, particularly in the case of blade cooling, combines a closed steam cooling system in the main part of the blade with an open cooling system in the region of the blade leading edge.
A gas turbine with a closed cooling system for the stator blades and rotor blades and also for the hot gas casing of the turbine has been proposed in U.S. Pat. No. 5,611,197, in which air at a specified pressure is extracted from the compressor at an intermediate pressure stage or at the exit, guided as cooling air through the components which are to be cooled, and then fed again at a suitable lower pressure stage into the compressor. The recirculated cooling air in this case can also be additionally cooled in a cooler before being fed into the compressor.
Also, a gas turbine with a partially closed cooling system is known from U.S. Pat. No. 7,263,834, in which a portion of the cooling air is used for the film cooling of the component surfaces which are exposed to the hot gas, and an additional portion of the cooling air is recirculated into the compressor.
For increasing power, water injection for intercooling between a low-pressure compressor and a high-pressure compressor is known from U.S. Pat. No. 6,012,279.
The addition of cooling air leads to mixing losses in the compressor and the water injection leads to mixing losses and increased overall length.